I’ve done quite a bit of developing and field-debugging with it. Haven’t had any complaints, beyond the unavoidable “My neck hurts.” and “Why is Windows choosing now to prompt me to use OneDrive, scan for viruses, update its search index, and install some mystery .NET runtime updates!? I only have 30% battery left!!”
I use it for school, coding, and editing my wife's photos she takes with her camera. It has been a very solid machine. My only wish would have been more RAM. When I upgrade I will probably get the Extreme so that I can edit videos and run more VMs. :)
It's so nice to just open up my laptop and have internet everywhere without the need to tether.
I think the X1 is a bit overrated - I prefer their T-series laptops for repairability and durability. You can generally pick some coming off of a corporate lease for a screaming deal.